/* s_atanf.c -- float version of s_atan.c.
 * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
 */

/*
 * ====================================================
 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
 *
 * Developed at SunPro, a Sun Microsystems, Inc. business.
 * Permission to use, copy, modify, and distribute this
 * software is freely granted, provided that this notice
 * is preserved.
 * ====================================================
 */

#include "math.h"
#include "float.h"

static const float atanhi[] = {
  4.6364760399e-01, /* atan(0.5)hi 0x3eed6338 */
  7.8539812565e-01, /* atan(1.0)hi 0x3f490fda */
  9.8279368877e-01, /* atan(1.5)hi 0x3f7b985e */
  1.5707962513e+00, /* atan(inf)hi 0x3fc90fda */
};

static const float atanlo[] = {
  5.0121582440e-09, /* atan(0.5)lo 0x31ac3769 */
  3.7748947079e-08, /* atan(1.0)lo 0x33222168 */
  3.4473217170e-08, /* atan(1.5)lo 0x33140fb4 */
  7.5497894159e-08, /* atan(inf)lo 0x33a22168 */
};

static const float aT[] = {
  3.3333328366e-01,
 -1.9999158382e-01,
  1.4253635705e-01,
 -1.0648017377e-01,
  6.1687607318e-02,
};

static const float one   = 1.0;
static const float huges   = 1.0e30;

float
atanf(float x)
{
    float w = 0, s1 = 0, s2 = 0, z = 0;
    int ix = 0, hx = 0, id = 0;

    GET_FLOAT_WORD(hx,x);
    ix = hx&0x7fffffff;
    if(ix>=0x4c800000) {    /* if |x| >= 2**26 */
        if(ix>0x7f800000)
        return x+x;        /* NaN */
        if(hx>0) return  atanhi[3]+*(volatile float *)&atanlo[3];
        else     return -atanhi[3]-*(volatile float *)&atanlo[3];
    } if (ix < 0x3ee00000) {    /* |x| < 0.4375 */
        if (ix < 0x39800000) {    /* |x| < 2**-12 */
        if((huges+x)>one) return x;    /* raise inexact */
        }
        id = -1;
    } else {
    x = fabsf(x);
    if (ix < 0x3f980000) {        /* |x| < 1.1875 */
        if (ix < 0x3f300000) {    /* 7/16 <=|x|<11/16 */
        id = 0; x = ((float)2.0*x-one)/((float)2.0+x);
        } else {            /* 11/16<=|x|< 19/16 */
        id = 1; x  = (x-one)/(x+one);
        }
    } else {
        if (ix < 0x401c0000) {    /* |x| < 2.4375 */
        id = 2; x  = (x-(float)1.5)/(one+(float)1.5*x);
        } else {            /* 2.4375 <= |x| < 2**26 */
        id = 3; x  = -(float)1.0/x;
        }
    }}
    /* end of argument reduction */
    z = x*x;
    w = z*z;
    /* break sum from i=0 to 10 aT[i]z**(i+1) into odd and even poly */
    s1 = z*(aT[0]+w*(aT[2]+w*aT[4]));
    s2 = w*(aT[1]+w*aT[3]);
    if (id<0) return x - x*(s1+s2);
    else {
        z = atanhi[id] - ((x*(s1+s2) - atanlo[id]) - x);
        return (hx<0)? -z:z;
    }
}

